Fungi as plant pathogens
Fungi cause rusts, smuts, mildews, rots, and wilts. They spread by spores via wind, water splash, insects, or contaminated seed.
Field symptoms vs signs
Symptoms are plant responses (yellowing, necrosis). Signs are pathogen structures (mold growth, rust pustules, concentric rings).
Diagnostic workflow
- Map distribution — random vs row pattern suggests soil-borne vs airborne.
- Inspect under moist conditions when fungal structures are visible.
- Collect samples in paper bags; refrigerate if shipping to lab.
- Prepare microscope slides with KOH to clear host tissue and highlight hyphae.
Common crop examples
Powdery mildew — white powder on leaf surfaces. Downy mildew — yellow patches with gray fuzz underneath. Fusarium wilt — vascular browning and one-sided leaf droop.